Migrate file picker from mpfilepicker to FileKit

[vinceglb]

MPFilePicker is now archived.

An alternative solution is to use FileKit:

• One of the benefits is that it targets Android, iOS, macOS, JVM and also WASM
• It uses native file system dialogs even on JVM thanks to JNA
• We can easily access file bytes from the common code

I thought it was a good idea to share this migration with you 😄

PS: I updated generative vision model because gemini-pro-vision is deprecated and returns an exception now.

[joreilly]

Nice cleanup!